Fundamental obstacle for electrical spin injection from a ferromagnetic metal into a diffusive semiconductor

We have calculated the spin-polarization effects of a current in a two-dimensional electron gas which is contacted by two ferromagnetic metals. In the purely diffusive regime, the current may indeed be spin-polarized. However, for a typical device geometry the degree of spin-polarization of the current is limited to less than 0.1% only. The change in device resistance for parallel and antiparallel magnetization of the contacts is up to quadratically smaller, and will thus be difficult to detect.